Karol Beck produced a superb display to end Tim Henman's hopes in the second round at Queen's.
Beck, who won last week's grass-court tournament at Surbiton, broke Henman twice to take the first set.
Henman then lifted himself and levelled the match by taking the second set with a single break of serve.
But he was never able to take full control, and Beck took the match to a deciding tie-break and came through a 6-2 3-6 7-6 (8/6) winner.
Henman will now have no more warm-up matches before Wimbledon gets under way in two weeks time, but he said the defeat did not concern him too much.
"I would have liked to have won more matches here," said Henman.
"I'm disappointed right now, but I'm sure that a week from Monday I'll be raring to go.
"I need to work on my transition to the grass, and I'll absolutely be doing that over the next 10 days."
Beck, meanwhile, described the win as "unbelievable".
"It's the best result of my career because Tim Henman is a great player," he said.
The unseeded Slovakian had never before beaten a top-10 player but cruised to the first set easily against the recent French Open semi-finalist.
The fourth seed rallied in set two but found himself staring at match point to Beck at 4-5 in the third.
The Englishman escaped and forced the tie-break but squandered a 4-2 lead to hand his opponent two more match points, the last of which Henman dumped into the net to seal the defeat.